Thermal diffusion method and apparatus



March 15, 195s Filed June 20, 1956 D. FRAzlER 2,827,171

THERMAL DIFFUSION METHOD AND APPARATUS 2 Sheets-Sheet 1 FEED RATE cc/mn.

INVENTOR. DAVID FRAZlER his A TORNEY March 18, 1958 D. FRAZIER 2,827,171

THERMAL' DIFFUSION METHOD AND APPARATUS Filed Junezm 195e 2 sheets-sheet2 IN VEN TOR. DAVID FRAZIER 5 ATTORNEY :United States Patent O THERPALD11? FUSN METHOD AND APPARATUS David Frazier, Cleveland Heights, Ohio,assignor to I1 he Standard @il Company, Cleveland, Ohio, a corporationof ho Application .lune 20, 1956, Serial No. 592,662

6 Claims. (Cl. 210-72) This invention relates to a continuous method andapparatus for separating uid mixtures into fractions enriched withdissimilar components.

lt has been ltnown for some time that it is possible to separate, bythermal diffusion, liquids and gases that are incapable of separation byany other known method, or that are separated by other methods withgreat difficulty. It was at first believed that thermal diffusion couldbe carried out only in a discontinuous, i. e., batchwise, manner. Morerecently, it has been discovered that it is possible to carry outthermal diffusion separation in a continuous manner.

The process of separation by thermal diffusion consists in essence ofconfining a fluid mixture, a term intended herein to include mixturesthat are liquid or gaseous under the conditions of operation, in anarrow chamber and imposing across the chamber a temperature gradient.When the opposed walls defining such a chamber are non-horizontal,thermal circulation of the contents of the chamber is set up by virtueof the differences in density adjacent the relatively heated and cooledwalls, referred to herein for convenience as the hot and cold Walls.This thermal circulation is relied upon to separate the components ofthe mixture that preferentially accumulate adjacent the hot wall fromthose components that preferentially accumulate adjacent the cold wall.

It has been found that in order to obtain satisfactory rates ofseparation by thermal diffusion, the opposed thermal diffussionchamber-forming surfaces of the hot and cold walls should be spacedapart no more than about one-half inch, spacings of the order of 0.2 to0.3 inch being preferred for separation of gaseous mixtures and smallerspacings of the order of 0.15 inch or less, preferably about 0.02 to0.06 inch, being most effective for separation of liquid mixtures. Inview of the small spacings involved, considerable diiculties have beenencountered in taking advantage of the separation actually, obtainedwithin a thermal diffusion separation chamber from the point of view ofseparately withdrawing the dissimilarl fractions formed within the verynarrow chamber and also inA replacing these fractions with fresh luidWithout undue turbulence and remixing of the separated fractions.

lt has now been found that surprisingly good yields of dissimilarfractions are obtainable, particularly at relatively high feed rates,with thermal diffusion separation chambers formed by non-horizontal,equidistantly-spaced wall members, e. g., substantially vertical,concentric tubes. These excellent results are obtainable by providingupper and lower reservoirs communicating with the upper and lower endsof the chamber and having Sullicient volume to permit mixing of freshfeed with fluids entering the reservoirs from the chamber and also toavoid a turnabout of the fluid within the separation chamber before itreaches the reservoir. Generally, these effects are obtained when thereservoirs are at least about twice as Wide and twice as high or deep asthe spacing between the walls forming the separation chamber,

By feeding the fresh fluid into the reservoirs, the separation chamberis lled with the fluid mixture which, by thermal diffusion, is separatedinto an ascending fraction containing a higher than initialconcentration of one of the dissimilar components and a descendingfraction containing a higher than initial concentration of another ofthe dissimilar components. The entering uid mixture is admixed in thereservoirs with these ascending and descending fractions andcontinuously withdrawn therefrom.

The apparatus and method of the invention land the surprisingly goodresults obtainable therewith are described in greater detail byreference to the accompanying drawing wherein:

Figure 1 is a schematic illustration, in elevation, of a prferredembodiment of the apparatus of the invention; `an

Figures 2 and 3 are graphs illustrative of the results obtainable wit-hthe method and apparatus of this invention as compared with thoseobtainable under com"arable conditions with apparatus in which theentire feed of fluid mixture enters the chamber midway between the upperand lower ends.

The apparatus illustrated in Figure l comprises an annular thermaldiffusion separation chamber 10 formed by the outer surface of an innertube 11 and the inner surface of an outer tube 12. The upper end of theannular chamber is provided with a reservoir 14 having an inletconnection 16 and an outlet connection 17. The lower end of the chamberis similarly provided with a reservoir 19 having an inlet connection 20and an outlet connection 21. Suitable means not forming part of thisinvention are provided for relatively heating and cooling thechamber-forming walls. Thus, for example, the inner tube 11 may berelatively heated by passing steam through it, and the outer tube 12 maybe relatively cooled by circulating water through la cooling jacket 22.

In operation, fresh liquid is continously introduced into upper andlower reservoirs 14 and 19 by way of inlet connections 16 and 20 and atemperature gradient is imposed across the separation chamber 10 byrelatively heating one of the inner and outer tubes and relativelycooling the other. The feed entering the reservoirs fills the thermaldiffusion chamber 10 and While therein is resolved into a first fractionaccumulating preferentially adjacent the hot wall ascending to the upperreservoir 14 and a second fraction accumulating preferentially adjacentthe cold wall and descending to the lower reservoir 19. Thus, forexample, if the inner tube 11 is relatively heated and the `outer tube12 is relatively cooled, the ascending fraction containing a higher thaninitial concentration of one of the dissimilar components in the liquidmixture ascends along the outer surface of the inner tube 11 and theother fraction containing a higher than initial concentration of anotherof the dissimilar components descends along the inner surface of theouter tube 12 into the lower reservoir 19. The fresh liquid mixtureentering the reservoirs is admixed with these dissimilar fractions, aportion of the liquid enters the separation chamber 10 to replace thefractions entering the reservoirs and the remainder, enriched with thecomponents in the dissimilar fractions, is separately withdrawn by wayof withdrawal ports 17 and 21.

A solvent extract neutral oil obtained by furfural extraction of an oilfrom a Mid-Continent crude and having a viscosity of SUS at 100 F. and arefractive index of 1.4730 was subjected to separation by thermaldiusion at varying rates of feed in an annular separation chamber suchas that illustrated in Figure 1 having a height of 6 feet, a meandiameter of one inch and a slit Patented Mar. 18, 1958 having a widthand height greater than the distance between said opposed walls,imposing a temperature gradient across the fluid in the chamber, wherebydissimilar fractions are formed, one of which contains a higher thaninitial concentration of one component and ascends to enter the upperreservoir and another of which contains a higher than initialconcentration of another component and descends to enter the lowerreservoir, continuously feeding fresh fluid into the upper and lowerreservoirs for admixture with the dissimilar fractions from said thermaldiffusion separation chamber, directing portions of the admixed iluid inthe respective reservoirs into the upper and lower ends of the thermaldiffusion separation chamber, and continuously and separatelywithdrawing dissimilar fractions from the upper and lower reservoirs.

4. Thermal diffusion method which comprises confining a liquid mixturein a vertical thermal diiusion separation chamber comprising opposedwalls and terminating in reservoirs at its upper and lower ends, saidreservoirs having a width and height greater than the distance betweensaid opposed walls, imposing a tempreature gradi- .ent across the liquidin the chamber, whereby dissimilar fractions are formed, one of whichcontains a higher than initial concentration of one component andascends to enter the upper reservoir and another of which contains ahigher than initial concentration of another component and descends toenter the lower reservoir, continuously feeding fresh liquid into theupper and lower reservoirs for admiXture with the dissimiiar fractionsfrom said thermal diffusion separation chamber, directing portions ofthe admixed liquid in the respective reservoirs into the upper and lowerends of the thermal diffusion separation chamber, and continuously andseparately withdrawing dissimilar fractions from the upper and lowerreservors.

5. Method for continuously separating a fluid mixture into fractionsenriched with dissimilar components which comprises imposing atemperature gradient across an annular separation chamber defined by theopposed 4 Walls of substantially vertical concentric tubes andcommunicating with upper and lower reservoirs at its upper and lowerends; said reservoirs having a width and height at least about twice thedistance between the opposed walls, continuously feeding fresh fluidinto said reservoirs, whereby the separation chamber is lled with huidmixture for separation into an ascending fraction containing a higherthan initial concentration of one of the dissimilar components and adescending fraction containing a higher than initial concentration ofanother of the dissimilar components and the entering fluid mixture isadmixed in said reservoirs with the ascending and descending fractions;and continuously and separately withdrawing, from the upper and lowerreservoirs, fractions enriched with dissimilar components by admixturewith the ascending and descending fractions.

6. Method for continuously separating a liquid mixture into fractionsenriched with dissimilar components which comprises imposing atemperature gradient across an annular separation chamber defined by theopposed walls of substantially vertical concentric tubes andcommunicating with upper and lower reservoirs at its upper and lowerends; said reservoirs having a width and height at least about twice thedistance between the opposed walls, continuously feeding fresh liquidinto said reservoirs, whereby the separation chamber is lled with liquidmixture for separation into an ascending fraction containing a higherthan initial concentration of one of the dissimilar components and adescending fraction containing a higher than initial concentration ofanother of the dissimilar components and the entering liquid ture isadmixed in said reservoirs with the ascending and descending fractions;and continuously and separately withdrawing, from the upper and lowerreservoirs, fractions enriched with disimilar components by adminturewith the ascending and descending fractions.

References Cited in the file of this patent UNITED STATES PATENTS

3. THERMAL DIFFUSILON METHOD WHICH COMPRISES CONFINING A FLUID MIXTUREIN A VERTICAL THERMAL DIFFUSION SEPARATION CHAMBER COMPRISING OPPOSEDWALLS AND TERMINATING IN RESERVOIRS AT ITS UPPER AND LOWER ENDS, SAIDRESERVOIRS HAVING A WILDTH AND HEIGHT GREATER THAN THE DISTANCE BETWEENSAID OPPOSED WALLS, IMPOSING A TEMPERATURE GRADIENT ACROSS THE FLUID INTHE CHAMBER, WHEREBY DISSIMILAR FRACTIONS ARE FORMED, ONE OF WHICHCONTAINS A HIGHER THAN INITIAL CONCENTRATION OF ONE COMPONENT ANDASCENDS, TO ENTER THE UPPER RESERVOIR AND ANOTHER OF WHICH CONTAINS AHIGHER THAN INITIAL CONCENTRATION OF ANOTHER COMPONENT AND DESCENDS TOENTER THE LOWER RESERVOIR, CONTINUOUSLY FEEDING FRESH FLUID INTO THEUPPER AND LOWER RESERVOIRS FOR ADMIXTURE WITH THE DISSIMILAR FRACTIONSFROM SAID THERMAL DIFFUSION SEPARATION CHAMBER, DIRECTING PORTIONS OFTHE ADMIXED FLUID IN THE RESPECTIVE RESERVOIRS INTO THE UPPER AND LOWERENDS OF THE THERMAL DIFFUSION SEPARATION CHAMBER, AND CONTINUOUSLY ANDSEPARATELY WITHDRAWING DISSIMILAR FRACTIONS FROM THE UPPER AND LOWERRESERVOIRS.